1. Field of the Invention
The present invention relates to a swash-plate operated type reciprocatory piston type compressor (hereinafter referred to as a swash plate type compressor) for use in air-conditioning systems for vehicles, and in particular, to an improved movable element lubricator incorporated into a swash plate type compressor for lubricating internal movable elements of the compressor, mainly thrust bearings, shoes, and swash plate, with a sufficient amount of lubricating oil even when the compressor is operated at a high speed.
2. Description of the Related Art
A typical swash plate type compressor as disclosed in, for example, U.S. Pat. No. 4,781,539 to Ikeda et al, is provided with a pair of horizontal axially aligned front and rear cylinder blocks which form a combined cylinder block, and the combined cylinder block is closed at both ends by front and rear housings, via valve plates. The front and rear housings form refrigerant suction chambers and refrigerant discharge chambers, and inside the combined cylinder block are formed a plurality of cylinder bores arranged around a central axis of the combined cylinder block and having axes in parallel with the central axis. Each of the cylinder bores is interconnected to the suction and discharge chambers of the front and rear housings. The combined cylinder block also has a centrally longitudinal bore formed therein, a drive shaft rotatably mounted therein via radial bearings, and a swash plate chamber in which a swash plate keyed on the drive shaft is rotatably received. The swash plate rotates with the drive shaft and is operatively engaged with double-headed pistons slidably fitted in the cylinder bores, to reciprocate the pistons across the swash plate chamber, i.e., shoes are arranged between the swash plate and the double-headed pistons to provide an universal coupling therebetween and to cause a reciprocatory compressing motion of the pistons within the cylinder bores in response to the rotation of the swash plate. Further, a pair of thrust bearings are arranged between axially opposite ends of the swash plate and the front and rear cylinder blocks to receive a thrust force acting on the swash plate as a reaction imposed by the reciprocatory motion of the pistons. Note, the reciprocatory pistons, the swash plate, the shoes, the thrust bearings, and the radial bearings are internal movable elements of the swash plate type compressor, and must be sufficiently lubricated by the lubricating oil. U.S. Pat. No. 4,781,539 discloses an example of a movable element lubricator, for a swash plate type compressor, incorporated in the swash plate type compressor for mainly lubricating the shoes and the swash plate of the compressor.
This swash plate type compressor is provided with a refrigerant circuit formed therein for introducing a refrigerant gas to be compressed from the air-conditioning circuit into the cylinder bores via the suction chambers, and for delivering a compressed refrigerant gas from the cylinder bores to the air-conditioning circuit via the discharge chambers, i.e., the refrigerant circuit includes a refrigerant circuit portion on the suction side, and a refrigerant circuit portion on the delivery side.
FIG. 6 illustrates another typical swash plate type compressor having front and rear cylinder blocks 1 and 2 axially combined and closed at both ends by front and rear housings 5 and 6, via valve plates 3 and 4. The front and rear cylinder blocks 1 and 2, and the front and rear housings 5 and 6 are axially combined together by an appropriate number of lengthy screw bolts (not illustrated in FIG. 6). The combined cylinder blocks are provided, at an axially central portion thereof, with a swash plate chamber 8 in which a swash plate 10 is received to be keyed on a drive shaft 9 rotatably mounted in centrally longitudinal coaxial bores 1a and 2a of the combined cylinder blocks 1 and 2, via a pair of front and rear radial bearings 22. A pair of thrust bearings 11 are arranged between opposite ends of boss 10a of the swash plate 10 and the inner ends of the front and rear cylinder blocks 1 and 2 to receive a thrust force acting on the swash plate 10 when the swash plate 10 rotates with the drive shaft 9 to reciprocate a plurality of double-headed pistons 13 within respective axial cylinder bores 12 of the combined cylinder blocks 1 and 2. The swash plate 10 is operatively engaged with the pistons 13 via shoes 14. The reciprocation of the double-headed pistons 13 compresses a refrigerant gas, and discharges the compressed refrigerant gas to be delivered from the compressor toward an air-conditioning circuit of a vehicle. The compressor of FIG. 6 is also provided with an oil pump 15 disposed inside the rear housing 6 and driven by the drive shaft 9, to thereby provide the thrust bearings 11 and the shoes 14 with a required amount of lubricating oil. That is, the lubricating oil is pumped out of an oil chamber 16 formed below the swash plate chamber 18 of the combined cylinder blocks 1 and 2, and supplied to a pump chamber 19 in the rear housing via an oil supply pipe 17 and an oil passage 18 formed in the rear valve plate 4. The lubricating oil is distributed from the pump chamber 19 to the thrust bearings 11 via an oil supply passage 20 bored in the drive shaft 9. The lubricating oil distributed to the thrust bearings 11 is further distributed to the shoes 14 and the swash plate 10 during the rotation of the swash plate 10. This oil distribution type lubricator employing the oil pump 15 is often incorporated in swash plate type compressors when a strong lubrication of the internal movable elements thereof is preferred.
Further, in another conventional oil lubricator of a swash plate type compressor, a lubricating oil is changed into oil mist by the rotation of the swash plate and is circulated with the refrigerant through a refrigerant circuit in the compressor, including suction chambers, a plurality of cylinder bores, and discharge chambers, and through a swash plate chamber for receiving therein a rotatable swash plate, so that the oil mist wets and lubricates the movable elements, such as the thrust bearings and the shoes.
In the swash plate type compressor illustrated in FIG. 6, during the compressing operation of the pistons 13, a part of the refrigerant gas compressed in the cylinder bores 12 leaks into the swash plate chamber 8, and therefore, a pressure level in the swash plate chamber 8 becomes higher than a suction pressure of the refrigerant. Nevertheless, from the point of view of lubricating the internal movable elements of the compressor, the pressure level in the swash plate chamber 8 is preferably equal to that of the suction pressure of the refrigerant gas. Although the swash plate chamber 8 is fluidly communicated with the suction chambers 21 of the front and rear housings 5 and 6, this fluid communication is not sufficient for lowering a pressure differential therebetween to zero. Therefore, one or more communicating holes are formed between the swash plate chamber 8 and a suction side of the compressor including the suction chambers 21 and suction passageways permitting the refrigerant gas before compression to flow from refrigerant inlet ports of the compressor toward the suction chambers 21.
When the rotating speed of the drive shaft 9 exceeds 5,000 R.P.M during the operation of the compressor, the pressure differential between the swash plate chamber 8 and the suction side of the compressor is increased. Also, in the construction of the compressor as illustrated in FIG. 6, the communicating passages between the swash plate 8 and the suction side of the compressor are relatively short. Therefore, the refrigerant gas containing therein a large amount of lubricating oil flows from the swash plate chamber 8 toward the suction chambers 21 through the refrigerant passageways. Therefore, an amount of lubricating oil supplied by the pump 15 becomes less than that carried from the swash plate chamber 8, and accordingly, the swash plate chamber 8 and the oil chamber 16 are not supplied with enough lubricating oil (i.e., a sufficient amount of lubricating oil is not reserved in the oil chamber 16) to thereby cause a lack of lubrication of the internal movable elements. Thus, a seizing of the shoes 14 as well as wear of the internal movable elements of the compressor, such as thrust bearings 11 and the radial bearings 22, occurs, and therefore, the operation life of the swash plate type compressor is eventually shortened.
Further, as a large amount of the lubricating oil carried from the swash plate chamber 8 toward the suction chambers 21 of the front and rear housings 5 and 6 is carried into the discharge chambers 23 of the front and rear housings when the refrigerant gas after compression is discharged into the discharge chambers 23, the lubricating oil is eventually delivered into the air-conditioning circuit connected to the swash plate type compressor, and therefore, the lubricating oil adheres to the outer surface of an evaporator of the air-conditioning circuit and adversely affects the operation of the evaporator.
In the case of the afore-mentioned conventional oil mist lubricator incorporated in the swash plate type compressors not employing an oil pump, when the lubricating oil together with the compressed refrigerant gas is delivered from the discharge chambers of the compressor into the air-conditioning circuit, the oil is separated from the compressed refrigerant gas by an oil filter, and the separated oil is returned to the suction side of the compressor to thereby prevent the lubricating oil from flowing into the air-conditioning circuit. Nevertheless, the filtering by the oil filter is often incomplete, and therefore, a considerable amount of the lubricating oil is directly delivered into the air-conditioning circuit with the compressed refrigerant gas, to adversely affect the operation of the evaporator and shorten the operating life of the air-conditioning circuit.